The Speed of Light

It is the astronomical speed limit for any object in this universe! Nothing can go faster than light. This might seem as a normal thing to most of you but in reality, it shapes our universe itself! Why is it so important though?

The speed of light was first calculated by Olaus Roemer, a Danish scientist who used his observations of Jupiter’s moons and their eclipses in 1676. His results were close, but not accurate. Note that the speed of light is always a constant, even for objects at motion… How?

Consider a bullet shot from a gun. If you have a vehicle which goes faster than it, then you can chase the bullet and catch it before it reaches the destination. Now, take a torch and switch it on. No matter how fast you travel to catch the first ray of that light, you can never ever reach it!

Why is it so? No one really knows why, practically. It is the ultimate and universal truth and we all are bound by it. But there are some reasons which might satisfy our curiosity.

To understand the concept of speed properly, we need to define what speed is. Speed is relative. One cannot simply define the speed of an object without a frame of reference. When I say I am at rest, I mean that with respect to a stationary object near me, I am not moving. Common sense, right? But things start getting concept once you realise that the Earth is spinning. The Earth is also revolving around the Sun. The Sun is moving around in our Milky Way. The Milky Way Galaxy itself is moving in the universe!

Nothing in this universe is at rest. So, measuring the speed of an object with respect to something ACTUALLY at rest is just impossible.

Light has a very special property when it comes to this. According to Einstein, be it with respect to whatever object in the cosmos, the speed of light is always a constant. So, if you measure the speed of light while at rest or while moving on a jet, the speed is always 29,97,92,458 m/s.

This is the reason why you can never catch light or overtake it! It is light’s very own property that sets this challenge! You might achieve 99.9% of the speed of light by luck and science, but that 0.1% can never be achieved.

What might actually happen if you achieve 99.9% of the speed of light? Well, things start to go crazy! The laws of classical physics start to break. You might also achieve immortality to a certain extent!

According to the theory of Special Relativity, when objects travel at high speeds, they become heavier. So, as the speed of the object reaches the speed of light, its mass increases abruptly. By common sense, to push heavier objects, we need more energy. If the mass is increasing abruptly without limits, the energy required to push that object becomes infinity. Practically and obviously, this isn’t possible!

Also, time doesn’t run the same for objects at light speed. In fact, time doesn’t run the same for anyone at motion. Time creates such complexities that some Physicists claim that time doesn’t exist at all. If you have seen Nolan’s masterpiece Interstellar, you would know what time-dilation is.

Let’s do a thought experiment to understand what time dilation is.
Twin A is on Earth with a clock synchronised to his brother’s clock. His brother twin B sets off on a spaceship which can travel at the speed of light. When the brothers say goodbye, their age is 10 years. After 10 years on B’s clock, he decides to return back. When he returns, he sees that his brother is in a wheelchair at the age of 95. The clocks are not the synchronised anymore.

Why is this happening? In fact, this phenomenon is true for every object at motion. Scientists have checked this with highly accurate atomic clocks on jet planes and have got results that confirm this phenomenon. Imagine, in the near future we might get to travel at high speeds and get to stay younger for a longer duration!

Time dilation occurs because the speed of light is same for the observer. So, the rate of time experienced by the observer changes with respect to objects moving at light speeds itself!

These are some of the things light does. It is still amazing to imagine what is beyond the speed of light. Afterall, this universe is limitless.

Next time you switch on a torch or light a lamp, realise that it will be the last time the first ray of light is with you. You will never catch it ever again…

Have a very Happy, Safe and Green Deepavali!

- Sameer V Devipur